On: ISO C became unusable for operating systems develo...

[foxfluff]

That's a nice example. It'd definitely be nice to have a warning for this one.

Fwiw GCC does have a related warning flag (-Wnull-dereference) but I'm not sure it's made exactly for this. I believe it works based on functions being annotated for possibly returning NULL, e.g. malloc. It's also not enabled by -Wall or -W because apparently there were too many false positives: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96554

I imagine patches would be welcome. I'm guessing there are more people who like to wish for more compiler features than there are people who like to develop compilers :)

[mzs → foxfluff]

edit: Thanks, I just checked and the warning doesn't work

https://godbolt.org/z/4TP1hfx4j

But your hint found -fno-delete-null-pointer-checks which does the trick

https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

And -fno-delete-null-pointer-checks made it into LLVM too. It's a good to know but a little late for when I needed it, cheers :)

  % cc -O3 -fno-delete-null-pointer-checks -Wall -Wextra -c foo.c
  % objdump -dr foo.o                                            
  
  foo.o: file format Mach-O 64-bit x86-64
  
  
  Disassembly of section __TEXT,__text:
  
  0000000000000000 _foo:
         0: 55                            pushq %rbp
         1: 48 89 e5                      movq %rsp, %rbp
         4: 48 85 ff                      testq %rdi, %rdi
         7: 74 04                         je 4 <_foo+0xd>
         9: 8b 07                         movl (%rdi), %eax
         b: 5d                            popq %rbp
         c: c3                            retq
         d: bf 02 00 00 00                movl $2, %edi
        12: e8 00 00 00 00                callq 0 <_foo+0x17>
    0000000000000013:  X86_64_RELOC_BRANCH _exit

[astrange → mzs]

If you want a general approach you can turn on ubsan in trap-only mode and see what traps have ended up in your output.